I, too, have had plenty of doctors tell me not to go into medicine. They were all of my parents' generation, and at first, I found it very discouraging. But when I sat back and thought about it, in some ways, they really got shafted. They started along this path back when the doctor was a highly respected (and highly paid) member of society, when paternalistic medicine was still enjoying its heyday, when technology was only just beginning to surge forward, and before HMOs and malpractice lawsuits were the rule rather than the exception. The landscape of medicine has changed completely, and now these doctors are practicing in a world they never conceived of when they applied.
Interestingly, the one doctor I worked with who ceaselessly encouraged me to go into medicine is the one doctor who never really worked in the "new" culture of medicine. Rather, she worked for Shriner's Hospitals, where she never had to worry about who had what insurance and who was getting billed. No matter what, her patients could get the care and referrals they needed, they could get it for free, and it was very comforting. And at the end of the day, she really and truly loved what she did, and she thought that I would love medicine too.
Anyway, my point is that I think a lot of doctors are unhappy that they're practicing in a different world than they thought they would be. We, on the other hand, are entering this field well aware of what the problems are, and we understand (I hope) what we're getting into. Sure, things might change on us the way they changed on the last generation of physicians, but I sincerely hope it'll be a change for the better rather than the worse. There is hope for us yet.